1. Field of the Invention
The invention relates to a hydraulic two-chamber bearing for damping vibrations, in particular an engine mount on motor vehicles, having an engine-mount plate, a bearing spring made of rubber-elastic material, a working chamber and a compensation chamber for the liquid which are separated from each other by a partition, and an elastic pressure diaphragm that terminates the compensation chamber.
2. Description of Related Art
DE 30 27 742 A1 describes a hydraulically damped two-chamber engine mount, which provides a high degree of damping at a low stiffness, in order to thereby achieve an increasing degree of damping at higher amplitudes and damp out large shocks in an optimum manner. However, the bearing should not react hydraulically to high-frequency, low-amplitude vibrations. For this purpose, the bearing is provided with an intermediate wall in the form of a partition, which reacts to high-frequency, low-amplitude vibrations, and is equipped with a choke or pressure-regulating valve that automatically closes at high pressures. Low amplitudes at a high frequency are damped by a suitable intermediate plate, without liquid being exchanged between the working chamber and the compensation chamber. However, vibrations having increasing amplitudes and a low frequency are increasingly damped by the increasing exchange of fluid. A disadvantage of this solution is that the bearing operates in a relatively narrow range. The method of operation of such a bearing is fixed by the geometry, mass, and stiffness of the vibratory systems used in the bearing. This means that, in each instance, such systems can only be designed for a particular loading case.
In order to achieve an improvement here, engine mounts were equipped with a damping mass. Such a bearing is described in DE 32 44 295 A1. It provides a bearing, in which high vibrational amplitudes of the engine are markedly damped, the maximum damping being adjustable to the natural frequency of the engine, and the hydraulic damping being decoupled at low amplitudes to yield an optimum acoustic response. The damping mass is operated by a permanent magnet having an electric coil, and an electrically controllable decoupling system is present, which allows an additional frequency range to be covered. The general disadvantage of such a bearing is that its action also has to be adjusted to predetermined frequency ranges, in order to be effective in them.
The requirements for an optimum engine mount result from the following two causes, namely the vibrational response of the vehicle body, which is subject to the road conditions, and secondly, the vibrational response of the engine itself, which is dependent on its operating states. Vibrations caused by unevenness of the road are in the low-frequency range of approximately 7 to 8 Hz, and have high amplitudes. In order to counteract this, the bearing should have a high stiffness with a high degree of damping. The damping is achieved by the column of liquid between the two chambers, and by the liquid present in the working chamber in conjunction with the bearing spring made of rubber-elastic material. The liquid flows from the working chamber into the compensation chamber and back, depending on the pressure direction.
The vibrations induced by the mover or driving motor are to be subdivided into two ranges, namely idling-range vibrations having an average frequency of 12 to 15 Hz and medium amplitudes, and vibrations during normal engine operation, which have a wide frequency range and low amplitudes. As a result, a low bearing stiffness with low damping is necessary in the idling range, while a very low bearing stiffness is expected during normal engine operation at higher frequencies. In this case, the bearing should be soft. The latter is attained through the vibrations of the diaphragms used.
In previous two-chamber engine mounts, regardless if they were designed to be passive or active, attention was payed to achieving a high degree of damping with a high bearing stiffness in the low-frequency range up to approximately 30 Hz, and a low stiffness in the frequency range above 30 Hz at low amplitudes. An example of a switchable bearing is known from DE 41 41 332 C2, which can switched over to various frequency ranges. The partition dividing up the chamber is provided with an opening, which can be closed by an actuator. The actuator is actuated by negative pressure and keeps the opening closed during operation. Such a switchable diaphragm can allow the bearing to achieve good working properties.
It is an object of the invention to provide a bearing design to first of all allow the option of more effectively adjusting the bearing to the vibration frequencies, and secondly render the bearing independent of negative-pressure control. It is a further object of the invention to provide such a bearing for use in diesel engines, where a high degree of damping is desired in the low-frequency range while idling, and where there are no negative-pressure devices for operating the bearing.
These and other objects of the invention are achieved by a hydraulic two-chamber bearing for damping vibrations, in particular an engine mount on motor vehicles, having an engine-mount plate, a bearing spring made of rubber-elastic material, a working chamber and a compensation chamber for the liquid which are separated from each other by a partition provided with flow-through openings, and an elastic pressure diaphragm which terminates the compensation chamber, wherein the amount of fluid flowing through the flow-through openings (6) of the partition (5) is controlled as a function of the amplitude (A) of the vibrations. The invention deviates from the previous bearing designs, which are directed towards damping low-frequency vibrations and providing high-frequency acoustic insulation, and replaces them with a two-chamber bearing, which is able to steplessly change from damping low-frequency, high amplitude vibrations to damping high-frequency, low-amplitude vibrations, so that a bearing can be manufactured, which ranges from having a high stiffness for the lowest frequencies up to the highest elasticity at the highest frequencies. This is achieved by controlling the amount of liquid flowing through the partition openings, as a function of the amplitude of the vibrations. The lower the frequency and the higher the amplitudes, the lower the amount of liquid flowing through the openings, and vice versa. This can be carried out to such an extent that the flow is completely blocked at the lowest frequencies, and the openings are completely unblocked at very high frequencies.